Powdered Milk

I've heard that Powdered Milk makes a nice amendment to soap. I may start using it, but have no idea how much to use.

Do you have experience adding powdered milk to soap? How much do you use? That is, how many grams of Powdered Milk per 100g of Distilled Water?

I would think it would be best to add it to the Sodium Hydroxide/Water mixture after that has cooled back down.